Loudspeaker

ABSTRACT

A loudspeaker includes an enclosure and at least one sound wave generator disposed in the enclosure. The sound wave generator includes at least one carbon nanotube structure. The carbon nanotube structure is capable of converting electrical signals into heat. The heat is transferred to a medium and causes a thermoacoustic effect.

RELATED APPLICATIONS

This application is related to a copending application entitled,“HEADPHONE”, filed ______ (Atty. Docket No. US20658).

BACKGROUND

1. Technical Field

The present disclosure relates to loudspeakers and, particularly, to acarbon nanotube based loudspeaker.

2. Description of Related Art

Loudspeakers are apparatus that reproduce sound recorded in differentmedia. The loudspeaker commonly includes an enclosure (i.e., housing,box, or cabinet) and a sound wave generator disposed in the enclosure.The loudspeakers can be divided into passive loudspeakers and activeloudspeakers. The active loudspeakers are any loudspeakers that containtheir own amplifiers (e.g. those for computers or i-pods), orloudspeakers that divide the frequencies for each sound wave generatorbefore power-amplification, using an active crossover. The passiveloudspeakers are loudspeakers without amplifiers.

The enclosure generally is a shell structure defining a hollow spacetherein, made of wood, ceramic, plastic, resin, or other suitablematerial. The sound wave generator inside the enclosure is used totransform an electrical signal into a sound pressure that can be heardby human ears.

There are different types of sound wave generators that can becategorized according by their working principle, such aselectro-dynamic sound wave generators, electromagnetic sound wavegenerators, electrostatic sound wave generators and piezoelectric soundwave generators. However, the various types ultimately use mechanicalvibration to produce sound waves, in other words they all achieve“electro-mechanical-acoustic” conversion. Among the various types, theelectro-dynamic sound wave generators are most widely used.

Referring to FIG. 19, a typical passive loudspeaker 10 according to theprior art with an electro-dynamic sound wave generator 100, includes anenclosure 110. The sound wave generator 100 is disposed in the enclosure110. The sound wave generator 100 is mounted on a front panel of theenclosure 110. The sound wave generator 100 includes a voice coil, amagnet and a cone. The voice coil is an electrical conductor, and isplaced in the magnetic field of the magnet. By applying an electricalcurrent to the voice coil, a mechanical vibration of the cone isproduced due to the interaction between the electromagnetic fieldproduced by the voice coil and the magnetic field of the magnets, thusproducing sound waves. However, the structure of the electric-poweredsound wave generator 100 is dependent on magnetic fields and oftenweighty magnets.

Carbon nanotubes (CNT) are a novel carbonaceous material and havereceived a great deal of interest since the early 1990s. Carbonnanotubes have interesting and potentially useful electrical andmechanical properties, and have been widely used in a plurality offields.

What is needed, therefore, is to provide a loudspeaker having a CNTstructure that is not dependent on magnetic fields.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present loudspeaker can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present loudspeaker.

FIG. 1 is a schematic structural view of a loudspeaker in accordancewith a first embodiment.

FIG. 2 is a schematic structural view of a carbon nanotube segment in adrawn carbon nanotube film.

FIG. 3 shows a Scanning Electron Microscope (SEM) image of the drawncarbon nanotube film of FIG. 2.

FIG. 4 shows an SEM image of another carbon nanotube film with carbonnanotubes entangled with each other.

FIG. 5 shows an SEM image of a carbon nanotube segment produced bypushing down a strip-shaped carbon nanotube array.

FIG. 6 shows an SEM image of an untwisted carbon nanotube wire.

FIG. 7 shows a SEM image of a twisted carbon nanotube wire.

FIG. 8 shows a textile formed by a plurality of carbon nanotube wirestructures or films.

FIG. 9 is a schematic structural view of one kind of sound wavegenerator in the loudspeaker of FIG. 1.

FIG. 10 is a schematic structural view of another kind of sound wavegenerator in the loudspeaker of FIG. 1.

FIG. 11 is a frequency response curve of a sound wave generatoraccording to one embodiment.

FIG. 12 is a block diagram of a circuit of the loudspeaker in FIG. 1.

FIG. 13 is a schematic structural view of a loudspeaker in accordancewith a second embodiment.

FIG. 14 is a schematic structural view of a loudspeaker with a framingelement in accordance with a second embodiment.

FIG. 15 is a schematic structural view of a loudspeaker in accordancewith a third embodiment.

FIG. 16 is a schematic structural view of a loudspeaker in accordancewith a fourth embodiment.

FIG. 17 is a schematic structural view of a loudspeaker in accordancewith a fifth embodiment.

FIG. 18 is a schematic structural view of a loudspeaker in accordancewith a sixth embodiment.

FIG. 19 is a schematic structural view of a conventional loudspeakeraccording to the prior art.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate at least one exemplary embodiment of the present loudspeaker,in at least one form, and such exemplifications are not to be construedas limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Reference will now be made to the drawings to describe, in detail,embodiments of the present loudspeaker.

Referring to FIG. 1, a closed box type loudspeaker 20 according to afirst embodiment includes an enclosure 210, and at least one sound wavegenerator 200. The enclosure 210 includes at least one first throughhole 212 (i.e., opening). Size of the sound wave generator 200 can besubstantially equal to or larger than the first through hole 212. Thesound wave generator 200 covers the first through hole 212. A closedhollow space is defined by the enclosure 210 and the sound wavegenerator 200. In one embodiment, the first through hole 212 is definedin a fore wall of the enclosure 210, and the sound wave generator 200 isinside the enclosure 210 and covers the first through hole 212. Air canpass through the sound wave generator 200.

The enclosure 210 can be made of a light-weight but strong material suchas wood, bamboo, carbon fiber, glass, diamond, crystal, ceramic, plasticor resin. The enclosure 210 can also comprise of a sound absorbingmaterial.

The sound wave generator 200 includes a carbon nanotube structure 202.The carbon nanotube structure 202 can have many different structures anda large specific surface area (e.g., above 50 m²/g). The heat capacityper unit area of the carbon nanotube structure 202 can be less than2×10⁻⁴ J/cm²·K. In one embodiment, the heat capacity per unit area ofthe carbon nanotube structure 202 is less than or equal to about1.7×10⁻⁶ J/cm²·K. In one embodiment, the sound wave generator 200 is acarbon nanotube structure 202 with a large specific surface areacontacting to the surrounding medium and a small heat capacity per unitarea, and the carbon nanotube structure 202 are composed of the carbonnanotubes.

The carbon nanotube structure 202 can include a plurality of carbonnanotubes uniformly distributed therein, and the carbon nanotubestherein can be combined by van der Waals attractive force therebetween.It is understood that the carbon nanotube structure 202 must includemetallic carbon nanotubes. The carbon nanotubes in the carbon nanotubestructure 202 can be arranged orderly or disorderly. The term‘disordered’ includes, but is not limited to, a structure where thecarbon nanotubes are arranged along many different directions, arrangedsuch that the same number of carbon nanotubes arranged along eachdifferent direction can be almost the same (e.g. uniformly disordered);and/or entangled with each other. ‘Ordered’ includes, but not limitedto, a structure where the carbon nanotubes are arranged in aconsistently systematic manner, e.g., the carbon nanotubes are arrangedapproximately along a same direction and or have two or more sectionswithin each of which the carbon nanotubes are arranged approximatelyalong a same direction (different sections can have differentdirections). The carbon nanotubes in the carbon nanotube structure 202can be selected from a group consisting of single-walled, double-walled,and/or multi-walled carbon nanotubes. It is also understood that theremay be many layers of ordered and/or disordered carbon nanotubes in thecarbon nanotube structure 202.

The carbon nanotube structure 202 may have a substantially planarstructure. The thickness of the carbon nanotube structure 202 may rangefrom about 0.5 nanometers to about 1 millimeter. The smaller thespecific surface area of the carbon nanotube structure 202, the greaterthe heat capacity will be per unit area. The larger the heat capacityper unit area, the smaller the sound pressure level of the acousticdevice.

In one embodiment, the carbon nanotube structure 202 can include atleast one drawn carbon nanotube film. Examples of a drawn carbonnanotube film (also known as a yarn) is taught by U.S. Pat. No.7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. The drawncarbon nanotube film includes a plurality of successive and orientedcarbon nanotubes joined end-to-end by van der Waals attractive forcetherebetween. The carbon nanotubes in the carbon nanotube film can besubstantially aligned in a single direction. The drawn carbon nanotubefilm can be formed by drawing a film from a carbon nanotube array thatis capable of having a film drawn therefrom. Referring to FIGS. 2 to 3,each drawn carbon nanotube film includes a plurality of successivelyoriented carbon nanotube segments 143 joined end-to-end by van der Waalsattractive force therebetween. Each carbon nanotube segment 143 includesa plurality of carbon nanotubes 145 parallel to each other, and combinedby van der Waals attractive force therebetween. As can be seen in FIG.3, some variations can occur in a drawn carbon nanotube film. The carbonnanotubes 145 in the drawn carbon nanotube film are also oriented alonga preferred orientation. The plurality of carbon nanotubes 145 joinedend-to-end to form the free-standing drawn carbon nanotube film. Freestanding includes films that do not have to be, but still can besupported. The carbon nanotube film also can be treated with an organicsolvent. After treatment, the mechanical strength and toughness of thetreated carbon nanotube film are increased and the coefficient offriction of the treated carbon nanotube films is reduced. The treatedcarbon nanotube film has a larger heat capacity per unit area and thusproduces less of a thermoacustic effect than the corresponding nontreated film. A thickness of the carbon nanotube film can range fromabout 0.5 nanometers to about 100 micrometers. The drawn carbon nanotubefilm is adhesive in nature. The single drawn carbon nanotube film has aspecific surface area of above about 100 m²/g.

The carbon nanotube structure 202 of the sound wave generator 200 canalso include at least two stacked carbon nanotube films. In otherembodiments, the carbon nanotube structure 202 can include two or morecoplanar carbon nanotube films or both coplanar and stacked films.Additionally, an angle can exist between the orientation of carbonnanotubes in adjacent films, stacked or adjacent. Adjacent carbonnanotube films can be combined only by the van der Waals attractiveforce therebetween. The number of the layers of the carbon nanotubefilms is not limited. However, as the stacked number of the carbonnanotube films increasing, the specific surface area of the carbonnanotube structure will decrease, and a large enough specific surfacearea (e.g., above 30 m²/g) must be maintained to achieve thethermoacoustic effect and produce sound effectively. An angle betweenthe aligned directions of the carbon nanotubes in the two adjacentcarbon nanotube films can range from above 0° to about 90°. When theangle between the aligned directions of the carbon nanotubes in adjacentcarbon nanotube films is larger than 0 degrees, a microporous structureis defined by the carbon nanotubes in carbon nanotube structure. Spaceexist between adjacent carbon nanotubes. The carbon nanotube structure202 in an embodiment employing these films will have a plurality ofmicropores. Stacking the carbon nanotube films will add to thestructural integrity of the carbon nanotube structure 202. In someembodiments, the carbon nanotube structure 202 has a free standingstructure and does not require the use of structural support.

In other embodiments, the carbon nanotube structure 202 includes aflocculated carbon nanotube film. Referring to FIG. 4, the flocculatedcarbon nanotube film can include a plurality of long, curved, disorderedcarbon nanotubes entangled with each other. A length of the carbonnanotubes can be above 10 centimeters. Further, the flocculated carbonnanotube film can be isotropic. The carbon nanotubes can besubstantially uniformly dispersed in the carbon nanotube film. Theadjacent carbon nanotubes are acted upon by the van der Waals attractiveforce therebetween, thereby forming an entangled structure withmicropores defined therein. It is understood that the flocculated carbonnanotube film is very porous. Sizes of the micropores can be less than10 micrometers. The porous nature of the flocculated carbon nanotubefilm will increase specific surface area of the carbon nanotubestructure 202. Further, due to the carbon nanotubes in the carbonnanotube structure 202 being entangled with each other, the carbonnanotube structure 202 employing the flocculated carbon nanotube filmhas excellent durability, and can be fashioned into desired shapes witha low risk to the integrity of carbon nanotube structure 202. Thus, thesound wave generator 200 may be formed into many shapes. The flocculatedcarbon nanotube film, in some embodiments, will not require the use ofstructural support due to the carbon nanotubes being entangled andadhered together by van der Waals attractive force therebetween. Thethickness of the flocculated carbon nanotube film can range from about0.5 nanometers to about 1 millimeter.

In other embodiments, the carbon nanotube structure 202 includes acarbon nanotube segment film that comprises of at least one carbonnanotube segment. Referring to FIG. 5, the carbon nanotube segmentincludes a plurality of carbon nanotubes arranged along a commondirection. In one embodiment, the carbon nanotube segment film cancomprise one carbon nanotube segment. The carbon nanotubes in the carbonnanotube segment are substantially parallel to each other, have analmost equal length and are combined side by side via van der Waalsattractive force therebetween. At least one carbon nanotube will spanthe entire length of the carbon nanotube segment, so that one of thedimensions of the carbon nanotube segment film corresponds to the lengthof the segment. Thus, the length of the carbon nanotube segment is onlylimited by the length of the carbon nanotubes.

In some embodiments, the carbon nanotube segment film can be produced bygrowing a strip-shaped carbon nanotube array, and pushing thestrip-shaped carbon nanotube array down along a direction perpendicularto length of the strip-shaped carbon nanotube array, and has a lengthranged from about 1 millimeter to about 10 millimeters. The length ofthe carbon nanotube segment is only limited by the length of the strip.A carbon nanotube segment film also can be formed by having a pluralityof these strips lined up side by side and folding the carbon nanotubesgrown thereon over such that there is overlap between the carbonnanotubes on adjacent strips.

In some embodiments, the carbon nanotube film can be produced by amethod adopting a “kite-mechanism” and can have carbon nanotubes with alength of even above 10 centimeters. This is considered by some to beultra-long carbon nanotubes. However, this method can be used to growcarbon nanotubes of many sizes. Specifically, the carbon nanotube filmcan be produced by providing a growing substrate with a catalyst layerlocated thereon; placing the growing substrate adjacent to theinsulating substrate in a chamber; and heating the chamber to a growthtemperature for carbon nanotubes under a protective gas, and introducinga carbon source gas along a gas flow direction, growing a plurality ofcarbon nanotubes on the insulating substrate. After introducing thecarbon source gas into the chamber, the carbon nanotubes starts to growunder the effect of the catalyst. One end (e.g., the root) of the carbonnanotubes is fixed on the growing substrate, and the other end (e.g.,the top/free end) of the carbon nanotubes grow continuously. The growingsubstrate is near an inlet of the introduced carbon source gas, theultra-long carbon nanotubes float above the insulating substrate withthe roots of the ultra-long carbon nanotubes still sticking on thegrowing substrate, as the carbon source gas is continuously introducedinto the chamber. The length of the ultra-long carbon nanotubes dependson the growth conditions. After growth has been stopped, the ultra-longcarbon nanotubes land on the insulating substrate. The carbon nanotubesare then separated from the growing substrate. This can be repeated manytimes so as to obtain many layers of carbon nanotube films on a singleinsulating substrate. The layers may have an angle from 0 to less thanor equal to 90 degrees between them by changing the orientation of theinsulating substrate between growing cycles.

The carbon nanotube structure 202 can further include at least twostacked or coplanar carbon nanotube segments. Adjacent carbon nanotubesegments can be adhered together by van der Waals attractive forcetherebetween. An angle between the aligned directions of the carbonnanotubes in adjacent two carbon nanotube segments ranges from 0 degreesto about 90 degrees. A thickness of a single carbon nanotube segment canrange from about 0.5 nanometers to about 100 micrometers.

Further, the carbon nanotube film and/or the entire carbon nanotubestructure 202 can be treated, such as by laser, to improve the lighttransmittance of the carbon nanotube film or the carbon nanotubestructure 202. For example, the light transmittance of the untreateddrawn carbon nanotube film ranges from about 70%-80%, and after lasertreatment, the light transmittance of the untreated drawn carbonnanotube film can be improved to about 95%. The heat capacity per unitarea of the carbon nanotube film and/or the carbon nanotube structure202 will increase after the laser treatment.

In other embodiments, the carbon nanotube structure 202 includes one ormore carbon nanotube wire structures. The carbon nanotube wire structureincludes at least one carbon nanotube wire. A heat capacity per unitarea of the carbon nanotube wire structure can be less than 2×10⁻⁴J/cm²·K. In one embodiment, the heat capacity per unit area of thecarbon nanotube wire structure is less than 5×10⁻⁵ J/cm²·K. The carbonnanotube wire can be twisted or untwisted. The carbon nanotube wirestructure can also comprised of twisted or untwisted carbon nanotubecables. These carbon nanotube cables can include twisted carbon nanotubewires, untwisted carbon nanotube wires, or combination thereof. Thecarbon nanotube wires in the carbon nanotube cables can be parallel toeach other to form a bundle-like structure or twisted with each other toform a twisted structure.

The untwisted carbon nanotube wire can be formed by treating the drawncarbon nanotube film with an organic solvent. In one embodiment, thedrawn carbon nanotube film is treated by applying the organic solvent tothe drawn carbon nanotube film to soak the entire surface of the drawncarbon nanotube film. After being soaked by the organic solvent, theadjacent paralleled carbon nanotubes in the drawn carbon nanotube filmwill bundle together, due to the surface tension of the organic solventwhen the organic solvent volatilizing, and thus, the drawn carbonnanotube film will be shrunk into untwisted carbon nanotube wire.Referring to FIG. 6, the untwisted carbon nanotube wire includes aplurality of carbon nanotubes substantially oriented along a samedirection (e.g., a direction along the length of the untwisted carbonnanotube wire). The carbon nanotubes are substantially parallel to theaxis of the untwisted carbon nanotube wire. Length of the untwistedcarbon nanotube wire can be set as desired. The diameter of an untwistedcarbon nanotube wire can range from about 0.5 nanometers to about 100micrometers. In one embodiment, the diameter of the untwisted carbonnanotube wire is about 50 micrometers. Examples of the untwisted carbonnanotube wire is taught by US Patent Application Publication US2007/0166223 to Jiang et al.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film by using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. Referring to FIG.7, the twisted carbon nanotube wire includes a plurality of carbonnanotubes oriented around an axial direction of the twisted carbonnanotube wire. Length of the carbon nanotube wire can be set as desired.The diameter of the twisted carbon nanotube wire can range from about0.5 nanometers to about 100 micrometers. Further, the twisted carbonnanotube wire can be treated with a volatile organic solvent. Afterbeing soaked by the organic solvent, the adjacent paralleled carbonnanotubes in the twisted carbon nanotube wire will bundle together, dueto the surface tension of the organic solvent when the organic solventvolatilizing. The specific surface area of the twisted carbon nanotubewire will decrease. The density and strength of the twisted carbonnanotube wire will be increase.

The carbon nanotube structure 202 can include a plurality of carbonnanotube wire structures. The plurality of carbon nanotube wirestructures can be parallel with each other, cross with each other,weaved together, or twisted with each other to form a planar structure.Referring to FIG. 8, a textile can be formed by the carbon nanotube wirestructures 146 and used as the carbon nanotube structure 202. Twoelectrodes 204 can be located at two opposite ends of the textile andelectrically connected to the carbon nanotube wire structures 146. It isalso understood that carbon nanotube films can be cross with each other,weaved together, twisted with each other to form a planar structure, orform a textile as shown in FIG. 8.

It is understood that the carbon nanotube structure 202 can include aplurality of micropores. Thus, air can pass through carbon nanotubestructure 202 between the outside and inside of the enclosure 210.

In the embodiment shown in FIG. 1, the sound wave generator 200 includesa carbon nanotube structure 202 comprising the drawn carbon nanotubefilm, and the drawn carbon nanotube film includes a plurality of carbonnanotubes arranged along a preferred direction. The length of the carbonnanotube structure 202 is about 5 millimeters, the width thereof isabout 3 millimeters, and the thickness thereof is about 50 nanometers.It can be understood that when the thickness of the carbon nanotubestructure 202 is small, for example, less than 10 micrometers, the soundwave generator 200 has greater transparency. Thus, it is possible toacquire a transparent loudspeaker 20 by employing a transparent carbonnanotube structure 202 comprising a transparent carbon nanotube film ina transparent enclosure 210.

The sound wave generator 200 can be fixed in the enclosure 210 byadhesive means such as a binder, or mechanical means. Because, some ofthe carbon nanotube structures 202 have large specific surface area,some of the carbon nanotube structure 202 can be adhered on theenclosure 210 merely by itself according to its adhesive nature.

It is to be understood that the loudspeaker 20 can include several soundwave generators disposed in the enclosure 210. The sound wave generatorscan in a carbon nanotube structure 202, electro-dynamic sound wavegenerators, electromagnetic sound wave generators, electrostatic soundwave generators and/or piezoelectric sound wave generators.

The loudspeaker 20 can further include wires (not shown) capable oftransmitting electrical signals.

The sound wave generator 200 can further include at least two spacedelectrodes 204 electrically connected to the carbon nanotube structure202. The electrodes 204 can be disposed and fixed on two opposite endsof the carbon nanotube structure 202. Each electrode 204 is connected toa wire and is used to receive the electrical signals from the wire andtransmit them to the carbon nanotube structure 202. In one embodiment,an amplifier is used to amplify the audio electrical signal includes twooutput ports. The two output ports are electrically connected to the twoelectrodes 204 by the wires. The amplified audio electrical signal istransmitted through the carbon nanotube structure 202 by the twoelectrodes 204. In another embodiment, one electrode receives an inputwhile the other electrode is grounded.

When the carbon nanotubes in the carbon nanotube structure 202 arealigned along a same direction (such as the carbon nanotubes in thedrawn carbon nanotube film or carbon nanotube segment film), theelectrodes 204 can be disposed at two opposite ends of the aligneddirection. Thus, the carbon nanotubes in the carbon nanotube structure202 are aligned along the direction from one electrode 204 to the otherelectrode 204. The electrode 204 can be strip shaped and parallel toeach other. The electrical signals are conducted to the carbon nanotubestructure 202. The carbon nanotubes in the carbon nanotube structure 202transform the electrical energy to the thermal energy. The thermalenergy heats the medium, changes the density of the air, and therebyemits sound waves. No movement is required by the sound wave generatorto create sound waves. Even if the sound wave generator is moving, ithas minimal effect on the sound waves produced.

Referring to FIG. 9, the carbon nanotube structure 202 can be a square,and the length of the strip shaped electrodes 204 can be equal to orlonger than the length of two opposite edges of the carbon nanotubestructure 202. Thus, when the electrodes 204 are disposed along theopposite edges of the carbon nanotube structure 202, all the carbonnanotube structure 202 can be electrically conductive, resulting inmaximum use of the entire carbon nanotube structure 202. In thisembodiment, the carbon nanotube structure 202 includes a drawn carbonnanotube film, and the carbon nanotubes in the carbon nanotube structure202 are aligned along the direction from one electrode 204 to the otherelectrode 204. It is also noted, that if there is a tear in the carbonnanotube structure 202, sound can still be produced as long as there issome connection between the two electrodes 204.

Referring to FIG. 10, the carbon nanotube structure 202 can be roundwith one electrode 204 disposed at the edge of the carbon nanotubestructure 202 and another electrode 204 disposed at the center of thecarbon nanotube structure 202. The carbon nanotube structure 202 canhave carbon nanotubes aligned radially from the center of the carbonnanotube structure 202. In one embodiment, a plurality of drawn carbonnanotube films or carbon nanotube wire structures can be radiallyarranged corresponding and to a round electrode 204 at a central point,wherein the drawn carbon nanotube films may have relatively narrowwidth.

The electrodes 204 are made of conductive material. The shape of theelectrodes 204 is not limited and can be selected from a groupconsisting of lamellar, rod, wire, block and other shapes. A material ofthe electrodes 204 can be selected from a group consisting of metals,conductive adhesives, carbon nanotubes, and indium tin oxides. In oneembodiment, the electrodes 204 are layer formed by silver paste.

In another embodiment, the electrodes 204 can be a metal rod and providestructural support for the carbon nanotube structure 202. Because, someof the carbon nanotube structures 202 have large specific surface area,some carbon nanotube structures 202 can be adhered directly to theelectrodes 204. This will result in a good electrical contact betweenthe carbon nanotube structures 202 and the electrodes 204. The twoelectrodes 204 can be electrically connected to two output ports of asignal input device by the wires (not shown) to receive the amplifiedsignals.

In other embodiment, a conductive adhesive layer (not shown) can befurther provided between the carbon nanotube structures 202 and theelectrodes 204. The conductive adhesive layer can be applied to thesurface of the carbon nanotube structures 202. The conductive adhesivelayer can be used to provide electrical contact and more adhesionbetween the electrodes 204 and the carbon nanotube structures 202. Inone embodiment, the conductive adhesive layer is a layer of silverpaste.

In addition, it can be understood that the electrodes 204 are optional.The carbon nanotube structures 202 can be directly connected to thesignal input device. Any way that can electrically connect the signalinput device to the carbon nanotube structures 202 and thereby inputelectrical signal to the carbon nanotube structures 202 can be adopted.

The carbon nanotube structure 202 is in communication with a surroundingmedium. Energy of the electrical signals is absorbed by the carbonnanotube structure 202 and the resulting energy will then be radiated asheat. This heating causes detectable sound signals due to pressurevariation in the surrounding (environmental) medium such as air. Thus athermal-acoustic effect is created. The input electrical signals can beaudio frequency electrical signals.

The carbon nanotube structure 202 includes a plurality of carbonnanotubes and has a small heat capacity per unit area and can have alarge area for causing the pressure oscillation in the surroundingmedium by the temperature waves generated by the sound wave generator200. In use, when signals, e.g., electrical signals, with variations inthe application of the signal and/or strength are input applied to thecarbon nanotube structure 202 of the sound wave generator 200, repeatedheating is produced in the carbon nanotube structure 202 according tothe variations of the signal and/or signal strength. Temperature waves,which are propagated into surrounding medium, are obtained. Thetemperature waves produce pressure waves in the surrounding medium,resulting in sound generation. In this process, it is the thermalexpansion and contraction of the medium in the vicinity of the carbonnanotube structure 202 that produces sound. This is distinct from themechanism of the conventional loudspeaker, wherein the pressure wavesare created by the mechanical movement of the diaphragm. Thus movementof the speaker will have minimal effect on sound produce when comparedto a conventional speaker relying on mechanical movement. The operatingprinciple of the sound wave generator 200 is “electrical-thermal-sound”conversion.

FIG. 11 shows a frequency response curve of the carbon nanotubestructure 202 including a single carbon nanotube film, and having alength and width of 30 millimeters. The carbon nanotube film in thisembodiment is a drawn carbon nanotube film. To obtain these results, analternating electrical signal with 50 voltages is applied to the carbonnanotube structure 202. A microphone was put in front of the carbonnanotube structure 202 at a distance of about 5 centimeters away fromthe carbon nanotube structure 202. As shown in FIG. 11, the carbonnanotube structure 202 has a wide frequency response range and a highsound pressure level. The sound pressure level of the sound wavesgenerated by the carbon nanotube structure 202 can be greater than 50 dBat a distance of 5 cm between the carbon nanotube structure 202 and amicrophone. The sound pressure level generated by the loudspeaker 20reaches up to 105 dB. The frequency response range of the carbonnanotube structure 202 can be from about 1 Hz to about 100 KHz withpower input of 4.5 W. The total harmonic distortion of this carbonnanotube structure 202 is extremely small, e.g., less than 3% in a rangefrom about 500 Hz to 40 KHz.

In one embodiment, the carbon nanotube structure 202 includes fivecarbon nanotube wire structures, and each of the carbon nanotube wirestructures includes a carbon nanotube wire. A distance between adjacenttwo carbon nanotube wire structures is 1 centimeter, and a diameter ofthe carbon nanotube wire structures is 50 micrometers, when analternating electrical signals with 50 voltages is applied to the carbonnanotube structure 202, the sound pressure level of the sound wavesgenerated by the loudspeaker 20 can be greater than about 50 dB, andless than about 95 dB. The sound wave pressure generated by theloudspeaker 20 reaches up to 100 dB. The frequency response range of oneembodiment loudspeaker 20 can be from about 100 Hz to about 100 KHz withpower input of 4.5 W.

Further, since the carbon nanotube structure 202 has an excellentmechanical strength and toughness, the carbon nanotube structure 202 canbe tailored to any desirable shape and size, allowing a loudspeaker ofmost any desired shape and size to be achieved.

Further, the loudspeaker 20 can include an audio crossover filter 230inside the enclosure 210. Referring to FIG. 12, the audio crossoverfilter 230 includes several output ends and an input end. The outputends are separately connected to corresponding sound wave generators200. The audio electrical signal is input to the audio crossover filter230 from the input end. The audio crossover filter 230 filters the audioelectrical signal into several bands, such as intermediate frequency,high frequency, and low frequency. The audio electrical signals indifferent bands are transmitted to different sound wave generators 200(such as a tweeter and a woofer).

Further, the active loudspeaker 20 can include an amplifying circuit 240and a power circuit 250 inside the enclosure 210. The power circuit 250and the amplifying circuit 240 are electrically connected therebetween.The power circuit 250 drives the amplifying circuit 240 to amplify theinput audio electrical signals. The amplifying circuit 240 is coupled tothe sound wave generator 200. In one embodiment, the amplifying circuit240 is electrically connected to the audio crossover filter 230. In use,the input audio electrical signals are amplified by the amplifyingcircuit 240 and transmitted to the audio crossover filter 230, and thentransmitted to the sound wave generator 200. The passive loudspeaker 20can be electrically connected to an amplifier outside the enclosure 210.

Referring to FIG. 13, a bass reflex type loudspeaker 30 according to asecond embodiment includes an enclosure 310, and at least one sound wavegenerator. 300 disposed inside the enclosure 310. The at least one soundwave generator 300 includes a carbon nanotube structure 302 and at leasttwo electrodes 304. The at least two electrodes 304 are spaced from eachother and electrically connected to the carbon nanotube structure 302.

The structure of the bass reflex type loudspeaker 30 in the secondembodiment is similar to the structure of the closed box typeloudspeaker 20 in the first embodiment. The difference is that the bassreflex type loudspeaker 30 further includes a duct 316 inside theenclosure 310. The duct 316 is connected to the enclosure 310. Morespecifically, the enclosure 310 includes at least one first through hole312 and at least one second through hole 314. The second through hole314 is defined through the duct 316. The sound wave generator 300 isassociated with the first through hole 314. In one embodiment, the soundwave generator 300 covers the first through hole 314.

The inside of the enclosure 310 communicates acoustically with theoutside through the through hole 314, via the duct 316. The duct 316 andthe interior of the enclosure 310 form a Helmholtz resonator withresonance frequency determined by the compliance of the air volumeinside the enclosure 310 and the air mass inside the duct 316.

Referring to FIG. 14, in one embodiment, the sound wave generator 300can be spaced from the first through hole 312. More specifically, thesound wave generator 300 can be fixed by a framing element 318 insidethe enclosure 310. The sound wave generator 300 is attached to theframing element 318, thus a portion of the sound wave generator 300 issuspended.

Referring to FIG. 15, a labyrinth type loudspeaker 40 according to athird embodiment includes an enclosure 410, and at least one sound wavegenerator 400 disposed inside the enclosure 410. The at least one soundwave generator 400 includes a carbon nanotube structure 402 and at leasttwo spaced electrodes 404 electrically connected to the carbon nanotubestructure 402.

The structure of the labyrinth type loudspeaker 40 in the thirdembodiment is similar to the structure of the closed box typeloudspeaker 20 in the first embodiment. The difference is that thelabyrinth type loudspeaker 40 further includes a plurality of partitions416 inside the enclosure 410. More specifically, the enclosure 410includes at least one first through hole 412 and at least one secondthrough hole 414. The partitions 415 in the enclosure 410 form alabyrinth between the sound wave generator 400 and the second throughhole 414. Sound passes through the labyrinth to the outside of theenclosure 410. The sound wave generator 400 faces the first through hole412. In one embodiment, the sound wave generator 400 covers the firstthrough hole 412. In another embodiment, the sound wave generator 400 isspaced from the first through hole 412.

Referring to FIG. 16, a passive radiator type loudspeaker 50 accordingto a fourth embodiment includes an enclosure 510 and at least one soundwave generator 500 disposed inside the enclosure 510. The at least onesound wave generator 500 includes a carbon nanotube structure 502 and atleast two spaced electrodes 504 electrically connected to the carbonnanotube structure 502.

The structure of the passive radiator type loudspeaker 50 in the fourthembodiment is similar to the structure of the closed box typeloudspeaker 20 in the first embodiment. The difference is that thepassive radiator type loudspeaker 50 further includes at least onepassive radiator 516 inside the enclosure 510. More specifically, theenclosure 510 includes at least one first through hole 512 and at leastone second through hole 514. The passive radiator 516 is mounted on thesecond through hole 514. In one embodiment, the passive radiator 516 isan electro-dynamic loudspeaker cone including a membrane made of paper,resin, fiber, carbon fiber, or combinations thereof. In one embodiment,the sound wave generator 500 covers the first through hole 512. Inanother embodiment, the sound wave generator 500 is spaced from thefirst through hole 512.

Referring to FIG. 17, a horn type loudspeaker 60 according to a fifthembodiment includes an enclosure 610, and at least one sound wavegenerator 600 disposed inside the enclosure 610. The at least one soundwave generator 600 includes a carbon nanotube structure 602 and at leasttwo spaced electrodes 604 electrically connected to the carbon nanotubestructure 602.

The structure of the horn type loudspeaker 60 in the fifth embodiment issimilar to the structure of the closed box type loudspeaker 20 in thefirst embodiment. The difference is that the horn type loudspeaker 60further includes a horn 616 inside the enclosure 610. More specifically,the horn 616 is mounted on the first through hole 612. The sound wavegenerator 600 covers the horn 616.

Referring to FIG. 18, a loudspeaker 70 according to a sixth embodimentincludes an enclosure 710, and at least one sound wave generator 700disposed inside the enclosure 710. The at least one sound wave generator700 includes a carbon nanotube structure 702 and at least two spacedelectrodes 704 electrically connected to the carbon nanotube structure702.

The structure of the loudspeaker 70 in the sixth embodiment is similarto the structure of the closed box type loudspeaker 20 in the firstembodiment. The difference is that the loudspeaker 70 further includes apassive radiator 716 inside the enclosure 710. More specifically, thepassive radiator 716 is mounted on the first through hole 712. Thepassive radiator 516 can be an electro-dynamic loudspeaker coneincluding a membrane made of paper, resin, fiber, carbon fiber, orcombinations thereof. The passive radiator 516 has an opening at thecenter. The sound wave generator 700 covers the opening of the passiveradiator 716.

It is to be understood that the present disclosure also refers to otherkinds of loudspeakers beside the above embodiments, that adopt a carbonnanotube structure in an enclosure thereof.

The sound wave generator in the loudspeaker employing the carbonnanotube structure does not require any magnet or other complicatedstructure. The structure of the loudspeaker is simple and decreases thecost of the production. Space in the enclosure is saved. Also theenclosures that use the carbon nanotube structure are not as required tobe as robust given that there is no dynamic stresses caused by movingparts, nor support of the extra weight required. The carbon nanotubestructure transforms the electric energy to heat that causes surroundingair expansion and contraction according to the same frequency of theinput signal and results a hearable sound pressure. Thus, theloudspeaker can work without a vibration film and the magnetic field.The carbon nanotube structure can provide a wide frequency responserange (1 Hz to 100 kHz), and a high sound pressure level. The carbonnanotube structure can be cut into any desirable shape and size thatmeet different needs of different kinds of loudspeakers. The carbonnanotube structure can be very small, and thus the size of theloudspeaker can be decreased and used in environments where traditionalloud speakers could not be employed. The carbon nanotube structure has alarge specific area, and is sticky in nature. The carbon nanotubestructure can be directly adhered on the inner wall of the enclosure.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the invention. Variations maybe made to the embodiments without departing from the spirit of theinvention as claimed. Elements associated with any of the aboveembodiments are envisioned to be associated with any other embodiments.The above-described embodiments illustrate the scope of the inventionbut do not restrict the scope of the invention.

1. A loudspeaker, the loudspeaker comprising: an enclosure; and at leastone sound wave generator disposed in the enclosure, wherein the soundwave generator comprising at least one carbon nanotube structure, thecarbon nanotube structure is capable of converting electrical signalsinto heat and transferring the heat to a medium to cause athermoacoustic effect.
 2. The loudspeaker of claim 1, wherein the carbonnanotube structure is free-standing.
 3. The loudspeaker of claim 1,wherein the carbon nanotube structure produces sounds in response to theelectrical signals, the electrical signals are capable of causing thecarbon nanotube structure to increase in temperature.
 4. The loudspeakerof claim 1, wherein the heat capacity per unit area of the carbonnanotube structure is less than or equal to 2×10⁻⁴ J/cm²·K.
 5. Theloudspeaker of claim 1, wherein the frequency response range of thesound wave generator ranges from about 1 Hz to about 100 KHz.
 6. Theloudspeaker of claim 1, wherein the carbon nanotube structure has asubstantially planar structure, and a thickness of the carbon nanotubestructure ranges from about 0.5 nanometers to about 1 millimeter.
 7. Theloudspeaker of claim 1, wherein the carbon nanotube structure comprisesa plurality of carbon nanotubes, and the carbon nanotubes are combinedby van der Waals attractive force therebetween.
 8. The loudspeaker ofclaim 7, wherein the carbon nanotubes are arranged in a substantiallysystematic manner.
 9. The loudspeaker of claim 7, wherein the carbonnanotubes are aligned substantially along a same direction.
 10. Theloudspeaker of claim 7, wherein the carbon nanotubes are joined end toend by van der Waals attractive force therebetween.
 11. The loudspeakerof claim 1, wherein the carbon nanotube structure comprises at least onecarbon nanotube film, at least one carbon nanotube wire, or at least onecarbon nanotube film and the at least one carbon nanotube wire.
 12. Theloudspeaker of claim 1, further comprising at least two electrodes, theat least two electrodes are located apart from each other andelectrically connected to the carbon nanotube structure.
 13. Theloudspeaker of claim 12, wherein the carbon nanotube structure comprisesa plurality of carbon nanotubes, the carbon nanotubes in the carbonnanotube structure are aligned along a direction from one electrode tothe other electrode.
 14. The loudspeaker of claim 1, wherein theenclosure comprises at least one through hole, and the sound wavegenerator covers the through hole.
 15. The loudspeaker of claim 1,wherein the enclosure comprises a framing element, the sound wavegenerator is attached to the framing element.
 16. The loudspeaker ofclaim 1, further comprising an audio crossover and a plurality of soundwave generators.
 17. The loudspeaker of claim 1, further comprising anamplifying circuit and a power circuit, the amplifying circuit isconnected to the power circuit and the sound wave generator.
 18. Theloudspeaker of claim 1, wherein the enclosure comprises at least oneelement of a group consisting of a duct, a partition, a passiveradiator, and a horn.